Battery cell thermal runaway barrier

ABSTRACT

A thermal runaway barrier for at least significantly slowing down a thermal runaway event within a battery assembly. The thermal runaway barrier includes a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers, thermally insulative inorganic particles of fumed silica dispersed within the fiber matrix, and a binder dispersed within the fiber matrix so as to hold together the fiber matrix. An optional organic encapsulation layer may also be used to encapsulate the nonwoven fibrous thermal insulation.

The present invention relates to a barrier for at least significantly slowing down a thermal runaway event within a battery assembly, e.g., like a battery assembly used in an electric vehicle.

BACKGROUND

Electric motors used in electric or hybrid vehicles (e.g., automobiles) are powered, at least in part, by batteries. Lithium ion batteries are typically used in such applications, and they are available in three forms: prismatic cells, pouch cells or cylindrical-shaped cells. These batteries are disposed within the vehicle compactly to save space. Sometimes one or more of the battery cells or battery modules experience a thermal runaway event, which can result in many if not all of the battery cells or battery modules overheating and being destroyed. There is a desire in the industry to prevent, stop or at least significantly slowing down such a thermal runaway event. The present invention is a contribution to that effort.

The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a thermal runaway barrier is provided that comprises a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers, thermally insulative inorganic particles comprising fumed silica dispersed within the fiber matrix, and a binder dispersed within the fiber matrix so as to hold together the fiber matrix. An optional organic encapsulation layer may also be included for enclosing the layer of nonwoven fibrous thermal insulation. An optional inorganic encapsulation layer may also be included for enclosing the layer of nonwoven fibrous thermal insulation.

In another aspect of the present invention, a battery cell module or assembly for an electric vehicle is provided. The battery cell module or assembly comprises a plurality of battery cells disposed in a housing, and a plurality of thermal runaway barriers according to the present invention. The battery cells are lined up in a row or stack, with one thermal runaway barrier being disposed between each pair of adjacent battery cells, or between a predetermined number of battery cells (e.g., after every third battery cell), or between battery modules.

In a further aspect of the present invention, a method is provided for making a thermal runaway barrier according to the present invention, where the method comprises forming the layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

BRIEF DESCRIPTION OF THE DRAWINGS

Descriptions corresponding to the included figures can be within this description.

FIG. 1 is a schematic end view of a fiber matrix layer and an optional encapsulation layer that may be used in a thermal runaway barrier application.

FIG. 2 is a schematic side view of a battery module of battery cells, with thermal runaway barriers disposed between adjacent battery cells.

FIG. 3 is a schematic top view of a battery pack of battery modules, with thermal runaway barriers placed between adjacent battery modules and/or on the top of the battery modules.

FIG. 4 is a photographic perspective view of a thermal runaway barrier encapsulated with an adhesive-backed organic polymeric layer with release liners and an expanding gas outlet/notch.

FIG. 5 is a schematic side view of a Dry-laid process for manufacturing a battery cell thermal runaway barrier, according to one embodiment of the present invention.

FIG. 6 is a cross-sectional view of one embodiment of a thermal runaway barrier showing multiple expanding gas vent holes formed through the encapsulating film, according to one embodiment of the invention.

FIG. 7 is a cross-sectional view of another embodiment of a thermal runaway barrier showing multiple expanding gas vent holes in the form of notches formed through the encapsulating film, according to another embodiment of the invention.

FIG. 8 is a top plan view of an additional embodiment of a thermal runaway barrier with two different types of expanding gas vent holes formed through the encapsulation film.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

In describing preferred embodiments of the invention, specific terminology is used for the sake of clarity. The invention, however, is not intended to be limited to the specific terms so selected, and each term so selected includes all technical equivalents that operate similarly.

As used herein, the terms “preferred” and “preferably” refer to embodiments described herein that can afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” or “the” component may include one or more of the components and equivalents thereof known to those skilled in the art. Further, the term “and/or” means one or all the listed elements or a combination of any two or more of the listed elements.

It is noted that the term “comprises” and variations thereof do not have a limiting meaning where these terms appear in the accompanying description. Moreover, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably herein. Relative terms such as left, right, forward, rearward, top, bottom, side, upper, lower, horizontal, vertical, and the like may be used herein and, if so, are from the perspective observed in the drawing. These terms are used only to simplify the description, however, and not to limit the scope of the invention in any way.

Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Where applicable, trade designations are set out in all uppercase letters.

The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements (e.g., preventing and/or treating an affliction means preventing, treating, or both treating and preventing further afflictions).

As used herein, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

“Ambient conditions” means at 25° C. and 101.3 kPa pressure.

“Average” means number average, unless otherwise specified.

“Continuous” means extending across a single, unified area along a given layer (a perforated sheet can be continuous);

“Cure” refers to exposing to radiation in any form, heating, or allowing to undergo a physical or chemical reaction that results in hardening or an increase in viscosity.

“Discontinuous” means extending across a plurality of discrete areas along a given layer, where the discrete areas are spaced apart from each other;

“Size” refers to the longest dimension of a given object or surface.

“Substantially” means to a significant degree, as in an amount of at least 50%, 60, 70, 80, 90, 95, 96, 97, 98, 99, 99.5, 99.9, 99.99, or 99.999%, or 100%.

“Thickness” means the distance between opposing sides of a layer or multilayered article.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range in increments commensurate with the degree of accuracy indicated by the end points of the specified range (e.g., for a range of from 1.000 to 5.000, the increments will be 0.001, and the range will include 1.000, 1.001, 1.002, etc., 1.100, 1.101, 1.102, etc., 2.000, 2.001, 2.002, etc., 2.100, 2.101, 2.102, etc., 3.000, 3.001, 3.002, etc., 3.100, 3.101, 3.102, etc., 4.000, 4.001, 4.002, etc., 4.100, 4.101, 4.102, etc., 5.000, 5.001, 5.002, etc. up to 5.999) and any range within that range, unless expressly indicated otherwise.

The term “polymer” will be understood to include polymers, copolymers (e.g., polymers formed using two or more different monomers), oligomers and combinations thereof, as well as polymers, oligomers, or copolymers that can be formed in a miscible blend.

The following Examples have been selected merely to further illustrate features, advantages, and other details of the invention. It is to be expressly understood, however, that while the Examples serve this purpose, the particular ingredients and amounts used as well as other conditions and details are not to be construed in a manner that would unduly limit the scope of this invention.

Referring to FIG. 1 , a fiber matrix layer 10 useful in a thermal runaway barrier application contains nonwoven inorganic (i.e., nonmetallic) or otherwise heat resistant fibrous insulation material, thermally insulative ceramic or otherwise nonmetallic inorganic particles, and an organic or inorganic binder. As used herein, nonmetallic means it is not a metal or metal alloy. Optionally, the fiber matrix layer 10 is encapsulated with an organic polymeric layer 12.

Referring to FIG. 2 , an exemplary battery module 20 includes an assembly of battery cells 22 and a plurality of thermal runaway barriers 24. Each thermal runaway barrier 24 can be in the form of one or more fiber matrix layers 10, with or without an encapsulation 12, and that can be made from the exemplary materials described herein. A thermal runaway barrier 24 can be disposed between adjacent battery cells 22, between groups of cells 22, or both, at one or more locations throughout the battery module 20. Typically, the battery module 20 rests above a cooling plate 26 and a tray 28.

Referring to FIG. 3 , an exemplary battery pack 30 includes a plurality of battery modules 20, which may each have its own cooling plate 26 and tray 28 or all of the modules 20 may share the same cooling plate 26 and tray 28. A thermal runaway barrier 24, formed from the exemplary materials described herein, can be disposed between one or more or all adjacent battery modules 20, on the top of one or more or all of the battery modules 20 (see reference number 24′), or any combination of both. A single or multiple thermal runaway barriers 24 may also be dimensioned so as to cover the tops of all of the battery modules 20.

Referring to FIG. 4 , an exemplary thermal runaway barrier 24 includes one or more fiber matrix layers (not shown) encapsulated with an organic polymeric layer 12 that covers both sides and the peripheral edge of the one or more fiber matrix layers. In one embodiment, the major opposite faces of the encapsulating layer 12 are coated with an adhesive (e.g., a pressure sensitive adhesive) protected by corresponding release liners 14 and 16. It is preferable for the encapsulating layer 12 to include one or more outlets or openings 18 (e.g., in the form of a notch) that allows air (e.g., hot air) or other gases to escape from inside the encapsulation 12, rather than cause the encapsulation 12 to swell and expand like a balloon, e.g., when the air trapped in the encapsulation 12 is heated to an elevated temperature (e.g., when the temperature of one or more of the adjacent battery cells 20 increases).

Referring to FIG. 5 , a conventional dry-laid manufacturing equipment and processes can be used to manufacture thermal runaway barriers 20 according to the invention. Examples of such equipment and processes can be found described in U.S. Pat. No. 9,580,848 (Henderson et al.), U.S. Pat. No. 9,475,034 (Vincent et al.), U.S. Pat. No. 7,491,354 (Anderson), and U.S. Pat. No. 6,808,664 (Falk et al.). Such equipment can include a chamber or forming box 40 with multiple feeder inlets, including an inlet 42 for feeding any desired combination of fibers, binder and particles into the box 40, and multiple inlets 44, 44′ and 44″ for feeding any desired number or type of filler materials into the box 40. After the fibers are combined and mixed together with the other ingredients, the resulting nonwoven fibrous material 45 is deposited onto a belt 46 that conveys the material 45 into, through and out of a baking oven 47 where the binder is cured at least so that the fibrous material 45 can be further processed. The resulting cured nonwoven fibrous material 45′ is then die-cut, laser-cut, water-jet cut, or otherwise processed into individual nonwoven fiber layers 10 (not shown), which are then processed at an encapsulation station 48, e.g., by having a polymeric film 12 (not shown) laminated to opposite sides of a single layer 10 or a stack of two or more layers 10. An optional hot melt adhesive or pressure sensitive adhesive can be applied to one or both sides of the encapsulate 12 at corresponding spray stations 49 and 49′. A protective release liner (not shown) can be subsequently applied to each adhesive surface.

Referring to FIG. 6 , one embodiment of a thermal runaway barrier 24 according to the invention includes one or more vent holes 52 formed through one or both layers of the encapsulating film 12. The vent holes 52 can have any desired shape (e.g., circular, rectangular, oval, etc.), and preferably the vent holes 52 are formed through a portion of the film 12 located beyond the periphery of the encapsulated fibrous layer(s) 10 and still within the periphery of the encapsulation 12, while also providing a path for expanding gases (e.g., air) to escape out of the space containing the fibrous layer(s) 10. The number, size and location of these vent holes 52 can vary as desired.

Referring to FIG. 7 , another embodiment of a thermal runaway barrier 24 according to the invention includes two vent holes 54, each in the form of a notch formed through the encapsulating film 12. The vent holes 54 can have any desired shape (e.g., semicircular, rectangular, semioval, etc.), and preferably the notches 54 are formed through a portion of the film 12 located beyond the periphery of the encapsulated fibrous layer(s) 10 and past the periphery of the encapsulation 12, while also providing a path for expanding gases (e.g., air) to escape out of the space containing the fibrous layer(s) 10. The number, size and location of these notches 54 can vary as desired.

Referring to FIG. 8 , an additional embodiment of a thermal runaway barrier 24 according to the invention includes two different types of vent holes 52 and 54 formed through the encapsulation 12, like those described above relative to FIGS. 6 and 7 .

TABLE 1 Test Materials Material Description Source AG Silica aerogel with a particle size of 100-700 micrometer and Cabot Corp, Boston, MA, a pore size of 20 nanometers available under the designation United States ENOVA Aerogel IC3110 EAF68 Aqueous polymer dispersed pressure sensitive adhesive Wacker Chemie AG, available under the designation VINNAPAS EAF 68 Vinyl München, Germany Acetate Ethylene EVERM Expanded vermiculite Sun Gro, Agawam, MA, United States EXP Sodium silicate intumescent powder available under the trade 3M Company, St. Paul, designation “EXPANTROL” MN, United States EXPERL Expanded perlite available under the designation EUROCELL Europerl, Pölten, Austria 300 FB Acrylic water-based spray adhesive available under the trade 3M Company designation “FASTBOND” 4224 NF FS Fumed silica with an average particle size of 0.2-0.3 Cabot Corp, Boston, MA, micrometers available under the trade designation CAB-O- United States SIL H-5 H2345 Hot melt pressure sensitive adhesive available under the Bostik, Inc, Milwaukee, designation THERMOGRIP H2345-E71 WI. United States K1 Soda-lime-borosilicate hollow glass microspheres with a 3M Company density of 0.125 g/cc and a median particle size of 65 micrometer available under the designation Glass Bubbles K1 LDM Alkaline earth silicate fiber with a mean fiber diameter of 3.0- Unifrax, Tonawanda, NY, 3.5 micrometer available under the designation SAFFIL LDM United States PA Copolyamide powder adhesive with a granular size of 100- Shaetti AG, Wallisellen, 500 micrometer available under the designation 5350 Switzerland PERL Raw, unexpanded perlite AGStein Aktiengesellschaft für Steinindustrie, Neuwied, Germany PP 0.02-millimeter polypropylene transparent film Charter-Nex Films, Superior, WI, United States SUM Alkaline earth silicate fibers, mean fiber diameter of 3-4 Nutec Fibratec, S.A. de micrometers, available under the trade designation NUTEC C.V., Mexico Supermag SW+ Alkaline earth silicate fibers with a mean fiber diameter of Morgan Advanced 2.5-3.4 micrometers available under the trade designation Materials, Windsor, United “SUPERWOOL PLUS” Kingdom T255 Polyester/polyethylene bi-component staple fibers, 1.3 dtex Trevira GmbH, Bobingen, and 6-millimeter length available under the trade designation Germany T255 VERM1 Vermucilite, 0.3-0.8 mm particle size Cometals, Inc, New York, NY, United States VERM2 Vermucilite 0.3-1.0 mm particle size Cometals, Inc, New York, NY, United States VERM3 Vermucilite 3.0-8.0 mm particle size Cometals, Inc, New York, NY, United States WDS Microporous inorganic silicate insulation available under the Morgan Advanced designation WDS ® Materials

Test Methods Hot-Side/Cold-Side Test 1 (HCST1)

In an MTS Insight 5 kN tensile test machine (obtained from MTS Insight of Eden Prairie, Minn., United States), a bottom platen was heated to 600° C., and a sample was placed on top of it. The upper platen, with a thermocouple embedded, was lowered such that the distance between the two platens was at 1.6 mm. The temperature increase at the cold-side was recorded with respect to time (continuously) until it reached 900 seconds (15 minutes).

Hot-Side/Cold-Side Test 2 (HCST2)

In a 10 kN tensile test machine (obtained from ZWICKROELL of Ulm, Germany), a top platen was heated to 600° C. and a sample was placed on a bottom platen with a thermocouple embedded set at ambient temperature. A heat shield was used to cover the sample to ensure that it stayed at ambient temperature. The heat shield was then removed, and the upper platen was lowered with pressure held at 1 MPa. The time the sample took reach a temperature of 150° C. (302° F.), designated t(150° C.), was recorded.

Shear Strength:

The methods of ASTM273C 273M were followed. A five-minute shear speed was used.

Thermal Conductivity Test:

Thermal conductivity measurements values were obtained using a Thermal Constants Analyzer, Model TPS 2500S obtained from Hot Disk® AB of Goteborg, Sweden. Measurements were taken by choosing the Isotropic/Bulk (Type I) module within the software. The measurements were run using a Kapton 5465 sensor (Hot Disk®) having a diameter of 3.2 mm. As specified by the manual, the samples should have a lateral dimension that is 1.5 to 2.0 times the radius of the sensor. The sample thickness should also be equivalent or greater than the radius of the sensor. To ensure that the thickness was sufficiently greater than the radius of the sensor, three to four layers of a sample were stacked on each side of the sensor and a small pressure was applied to ensure that layers were all in contact with one another.

Specified parameters were 1) measurement time in seconds and 2) heating power in mW. The sample temperature was inputted as the ambient room temperature. The measurement was then executed as defined in the TPS Manual.

The results were analyzed by clicking on “Calculate” within the software and selecting the “Standard Analysis” option. After the measurement, several graphs were presented by the software, including the “Transient” graph and the “Residual” graph. The transient graph displays the temperature increase of the sensor during the heating of the sample up to 200 points. The first pass at analyzing the results will start at point 10 and include everything up to point 200 on the transient. If the residual graph does not look like a random scatter of points, a smaller subset of datapoints was used for the analysis. This was done by trimming points from the beginning and end of the measurement. As a rule, the result was not reliable if less than 50 points are used in the analysis. In addition to satisfying the quality of the residual plot, several other numerical requirements were defined including “probing depth (PD)”, “temperature increase (TI)”, “total to characteristic time (TCT)”, and “mean deviation (MD)” as specified in the manual. For these specifications: the PD must be less than the thickness of the sample, the TI must be between 0.4 K and 4.0 K, the TCT must be between 0.33 and 1.0, and the MD must be a magnitude of 10-4 or better. If these five criteria were not met, the heating power and measurement times were adjusted. The settings were iterated until an accurate measurement was made, where accuracy was defined by satisfying all the numerical requirements laid out in the manual. Thermal conductivity values in W/m·K were measured and recorded for tested samples.

Examples 1-8 (EX1-EX8) and Comparative Examples 1-2 (CE1-CE2)

For Examples 1, 3, and 5-7, combinations of staple fibers by weight percent (as identified in Table 2) were weighed and premixed by hand before placing on top of a feeding belt. The fiber material was processed (i.e., fed from the top) through an air-laid processer, like that disclosed in U.S. Pat. No. 7,491,354, where the fibers were opened and dispersed into an air stream, then collected on a screen belt. Details of such air-laid processing apparatus and methods of using such apparatus in forming air-laid webs can be found described in U.S. Pat. No. 9,580,848 (Henderson et al.), U.S. Pat. No. 9,475,034 (Vincent et al.), U.S. Pat. No. 7,491,354 (Anderson), and U.S. Pat. No. 6,808,664 (Falk et al.). Fillers by weight percent (as identified in Table 2) were top or side fed into the chamber or forming box of the air-laid processor. A volumetric feeder coupled with an air-driven horn was used to distribute the fillers into the web uniformly. The sample was then sent through a forced-air convection oven at 143.3° C. (290° F.) at a speed of 1.1 m/min.

For Examples 2 and 4, the process described in Example 1 of U.S. Pat. No. 5,869,010 (Langer) was followed. Samples were assembled containing fibers and fillers by weight percent as identified in Table 2 rather than the materials identified in U.S. Pat. No. 5,869,010.

For Example 8, Example A of U.S. Pat. No. 9,399,864 (Samanta et al.) was followed with noted modifications. An aerogel slurry was prepared by adding 400 grams of Barlox 12 (obtained from Lonza Group of Basel, Switzerland) to 379 liters (100 gallons) of water at 43° C. (110° F.). The slurry was mixed. 200 grams of Foamaster 111 (obtained from BASF Group of Ludwigshafen, Germany) was added and the slurry was mixed. EAF68 by weight percent (as identified in Table 2) was added and mixed. AG by weight percent (as identified in Table 2) was then added and mixed. The slurry was mixed for fifteen minutes and 200 grams of MOJO MP 9307C was added and mixed. A fiber slurry was prepared by adding 717 grams of Microstrand 110X-481 (obtained from John Manville of Denver, Colo., United States) to 2271 liters (600 gallons) of water. The slurry was pulped for 60 seconds at 500 rpm. T255 by weight percent (as identified in Table 2) was added and the slurry was pulped for 30 seconds at 500 rpm. Another 1136 liters (300 gallons) of water was added to the slurry. 757 liters (200 gallons) of the fiber slurry was mixed with 379 liters (100 gallons) of the aerogel slurry and SW+ by weight percent (as identified in Table 2) was mixed in. The combined slurry was processed on a papermaking machine.

TABLE 2 Sample Compositions (Weight Percent) SW+ LDM T255 EAF68 PA AG K1 WDS EXP EX1 20 20 16 0 4 40 0 0 0 EX2 0 62 0 8 0 0 30 0 0 EX3 20 20 16 0 4 0 0 40 0 EX4 0 52 0 8 0 0 0 0 40 CE1 35 35 30 0 0 0 0 0 0 EX5 15 15 30 0 0 40 0 0 0 CE2 92 0 8 0 0 0 0 0 0 EX6 72 0 8 0 0 20 0 0 0 EX7 52 0 8 0 0 40 0 0 0 EX8 59.5 0 2.5 8 0 30 0 0 0 The samples underwent HCST1 testing and the results are represented in Table 3.

TABLE 3 Hot-side/Cold-side Temperature Test Results (Basis Weight = 600 gsm) in Celsius (° C.) Time (Minutes) EX1 EX2 EX3 EX4 CE1 EX5 CE2 EX6 EX7 EX8 0 22.0 22.0 22.0 22.0 22.0 22.0 33.9 24.3 29.5 35.0 1 45.9 67.3 56.3 81.0 68.9 48.6 53.4 46.8 44.5 58.0 2 63.1 87.3 78.3 103.0 94.7 67.8 68.8 62.6 55.5 73.7 3 76.9 103.8 95.6 120.3 114.0 80.7 80.9 75.4 64.2 87.1 4 88.0 117.5 108.6 136.5 129.0 92.3 90.4 85.6 71.1 98.0 5 96.7 127.1 118.8 146.6 140.7 101.6 94.5 90.0 74.0 106.7 6 104.4 134.6 126.5 155.3 150.5 109.5 101.6 97.2 79.3 113.9 7 110.0 140.8 133.1 162.1 158.0 115.4 110.3 105.8 85.5 120.1 8 115.3 145.7 138.5 168.1 164.6 119.6 114.9 110.2 88.8 125.3 9 119.2 150.0 143.1 173.0 169.9 124.6 118.9 113.9 91.7 129.7 10 122.6 153.7 147.0 177.3 174.5 128.1 122.2 117.0 94.1 133.6 11 125.7 157.0 150.5 181.3 178.5 131.5 125.2 119.7 96.1 137.0 12 128.4 159.8 153.4 184.5 181.9 131.9 127.6 121.9 97.8 139.9 13 130.8 162.4 156.1 187.5 184.9 140.2 129.8 124.0 99.3 142.6 14 132.8 164.6 158.6 190.0 187.5 137.7 131.8 125.8 100.6 145.0 15 134.7 166.5 160.8 192.0 189.9 141.2 133.6 127.4 101.8 147.1

Examples 9-34 (EX9-EX34) and Comparative Examples 3-8 (CE3-CE8)

The ‘General Procedure for Preparing Fibrous Sheet’ as described in U.S. Patent Application No. 2010/0115900 with material substitution as identified in Table 4 was followed. Tap water (3 liters, 18° C.) and 60 grams (g) of inorganic fibers and cleaned to a shot content of less than 50 percent by weight) were added to a GT800 Classic blender (obtained from Rotor Lips Ltd, Uetendorf, Switzerland). The blender was operated on low speed for five seconds. The resultant slurry was rinsed into a RW16 mixing container equipped with a paddle mixer (obtained from IKA-Werke GmbH, Staufen, Germany) using one liter of tap water (18° C.). The slurry was diluted with an additional one liter of tap water (18° C.). The diluted slurry was mixed at medium speed to keep solids suspended. Defoaming agent (obtained under the trade designation “FOAMASTER 111” (0.3 g) from Henkel, Edison, N.J.) and ethylene-vinyl acetate terpolymer latex (obtained under the trade designation “AIRFLEX 600BP” (6.0 g, 55 percent by weight solids) from Air Products were added. Flocculent is added dropwise in amounts as indicated in Table 4. Thermally insulative particles were then added as indicated in Table 4. The mixer speed was increased and mixing continued for from 1 to 5 minutes. The paddle mixer was removed, and the slurry was poured into a 20 cm×20 cm (8 inches×8 inches) sheet former (obtained from Williams Apparatus Co, Watertown, N.Y., United States) and drained. The surface of the drained sheet was rolled with a rolling pin to remove excess water. Then, the sheet was pressed between blotter papers at a surface pressure of 90-97 kPa (13-14 psi) for five minutes. The sheet was then dried at 150° C. in a forced air oven for 10-15 minutes and allowed to equilibrate overnight while exposed to the ambient atmosphere. The thickness and basis weight of the samples were measured at a constant pressure of 4.9 kPa, and are recorded in Table 5. For Examples 15-25 (EX15-EX25) the vermiculite material used in these samples were either pre-heated to permanently pre-expand the vermiculite, before being used to make the samples, or post-heated to permanently post-expand the vermiculite, after the samples were made, at specific time and temperature conditions. For EX21, the vermiculite was pre-heated at 300° C. for 6 hours before sample assembly. For EX22 and EX23, the vermiculite was heated at 450° C. for 30 minutes after sample assembly. For EX24, the vermiculite was pre-heated at 500° C. for 30 minutes before sample assembly. For EX25, EX33, and EX34. the vermiculite in the sample was pre-heated at 1000° C. for 30 minutes before sample assembly.

TABLE 4 Sample Compositions (Weight Percent) SW+ SUM EAF68 VERM1 EXVERM PERL EXPERL CE3 95 0 5 0 0 0 0 CE4 90 0 10 0 0 0 0 CE5 90 0 10 0 0 0 0 CE6 90 0 10 0 0 0 0 CE7 90 0 10 0 0 0 0 CE8 90 0 10 0 0 0 0 EX9 50 0 5 45 0 0 0 EX10 50 0 5 45 0 0 0 EX11 50 0 5 45 0 0 0 EX12 50 0 5 45 0 0 0 EX13 50 0 5 45 0 0 0 EX14 50 0 5 45 0 0 0 EX15 0 50 5 0 45 0 0 EX16 0 50 5 0 45 0 0 EX17 0 50 5 0 45 0 0 EX18 0 50 5 22.5 22.5 0 0 EX19 65 0 5 0 30 0 0 EX20 65 0 5 0 30 0 0 EX21 50 0 5 0 45 0 0 EX22 50 0 5 0 45 0 0 EX23 50 0 5 0 45 0 0 EX24 50 0 5 0 45 0 0 EX25 50 0 5 0 45 0 0 EX26 0 23 8 0 0 0 69 EX27 0 23 8 0 0 0 69 EX28 0 23 8 0 0 0 69 EX29 0 47 6 0 0 0 47 EX30 0 22 6 0 0 0 72 EX31 0 70 5 0 0 25 0 EX32 0 20 5 0 0 75 0 EX33 65 0 5 0 30 0 0 EX34 65 0 5 0 30 0 0 The samples underwent HCST2 testing, and the results are represented in Table 5.

TABLE 5 Hot-side/Cold-side Temperature Test Results Thickness Basis Weight t(150° C.) (mm) (gsm) (seconds) CE3 4.17 643 297 CE4 2.68 413 162 CE5 2.14 319 122 CE6 1.16 207 63 CE7 1.23 193 63 CE8 1.04 161 52 EX9 4.17 643 297 EX10 2.74 614 182 EX11 2.53 530 154 EX12 1.73 394 111 EX13 1.42 310 89 EX14 1.23 252 73 EX15 4.70 529 126 EX16 2.15 437 109 EX17 1.70 478 113 EX18 1.95 499 105 EX19 4.22 453 120 EX20 5.45 606 197 EX21 1.85 362 129 EX22 2.87 490 205 EX23 2.68 508 207 EX24 1.92 341 127 EX25 4.40 514 197 EX26 4.59 208 208 EX27 3.25 120 120 EX28 3.74 186 186 EX29 3.82 115 115 EX30 2.59 100 100 EX31 2.00 540 97 EX32 2.62 1197 139 EX33 2.80 450 116 EX34 3.42 550 141

Example 35 (EX35)

PP was laminated onto a sample as assembled in Example 5. Hand samples were hot pressed at 132° C. (270° F.) and 200 kPa on both sides. The edges were manually sealed using an impulse sealer which was at 149° C. (300° F.), and heated for 2 seconds, cooled for 10 seconds, with all the steps being conducted under a compressive force of 524 kPa (76 psi) pressure. The PP film thickness was 0.02 mm (1 mil). The 600 gsm sample underwent Shear Strength testing and the results are represented in Table 6.

Example 36 (EX36)

Hot melt adhesive H2345 was applied to the sample in Example 35 using a Nordson Altablue Gridmelter with a 15.24 cm (6 inch) melt blown adhesive die. The adhesive was heated at 193° C. (380° F.) and sprayed on to the web at 206.8 kPa (30 psi) air pressure and 20 RPM pump rate. The 600 gsm sample underwent Shear Strength testing and the results are represented in Table 6.

Example 37 (EX37)

FB was spray coated onto a sample as assembled in Example 35 using a ACCUSPRAY ONE Spray Gun System with PPS obtained from 3M Company of St. Paul, Minn., United States. Hand samples were spray coated on one side and then flipped to coat the other side. The 600 gsm sample underwent Shear Strength testing and the results are represented in Table 6.

Example 38 (EX38)

PKHH Phenoxy Resin obtained from Gabriel Performance Products of Akron, Ohio, United States was dissolved in a 50% solution of methyl ethyl ketone (MEK) to create an adhesive. The MEK was evaporated at room temperature for 60 minutes. Two coatings of the adhesive were applied onto one side of a 0.076 mm (3 mil) PET film obtained from Dupont of Wilmington, Del., United States. Two coatings of the adhesive were applied onto a side of another 0.076 mm (3 mil) PET film. The thickness of the adhesive coating was 0.036 mm (1.4 mil). The adhesive coated PET sample films were placed onto the top and bottom side of a sample as assembled in Example 5. The 600 gsm sample underwent Shear Strength testing and the results are represented in Table 6.

TABLE 6 Encapsulated Sample Test Results Shear Strength Example MPa EX35 0.27 EX36 0.27 EX37 0.26 EX38 1.28

Examples 39-40 (EX39-EX40)

Samples were assembled using procedures described in Examples 9-16 with the materials identified in Table 7. The thickness and basis weight of the samples were measured at a constant pressure of 4.9 kPa and are recorded in Table 8. The samples underwent HCST2 testing and the results are represented in Table 8.

TABLE 7 Sample Compositions (Weight Percent) SW+ EAF68 VERM2 VERM3 EX39 50 5 45 0 EX40 50 5 0 45

TABLE 8 Hot-side/Cold-side Temperature Test Results Thickness Basis Weight t(150° C.) (mm) (gsm) (seconds) EX39 1.78 405 84.7 EX40 2.65 723 413.8

Examples 41-57 (EX41-EX57)

Combinations of staple fibers by basis weight (as identified in Table 9) were weighed and processed through an air-laid processer. Details of the apparatus and methods of using the apparatus in forming air-laid webs are described in U.S. Pat. No. 9,580,848 (Henderson et al.), U.S. Pat. No. 9,475,034 (Vincent et al.), U.S. Pat. No. 7,491,354 (Anderson), and U.S. Pat. No. 6,808,664 (Falk et al.). The combined staple fibers were then processed again by the air-laid processor and a fumed silica filler was directly fed into the chamber of the air-laid processor by basis weight (as identified in Table 2). A screw feeder was used to distribute the fillers into the web uniformly. The web was sent through a forced-air convection oven at 148.89° C. (300° F.) at a speed between 0.25 m/min and 1.5 m/min. The thickness of the samples was between 0.5 to 15 mm.

The webs were then densified to a specified gap thickness using a hot press. Polytetrafluoroethylene (PTFE) coated fiberglass fabric sheets (obtained from McMaster-Carr of Elmhurst, Ill. United States) were placed on both sides of the samples and the samples were placed between two hot plates maintained at a temperature of 148.89° C. (300° F.). Pressure was applied for 30 to 120 seconds to activate the bi-component fibers (T255). The densified sample was then immediately placed between two plates maintained at room temperature under a pressure for 30 to 120 seconds, to set the web to the desired thickness.

TABLE 9 Sample Compositions (gsm) SW+ T255 FS EX41 256 64 80 EX42 192 48 160 EX43 128 32 240 EX44 384 96 160 EX45 288 72 320 EX46 192 48 480 EX47 640 160 200 EX48 480 120 400 EX49 480 120 400 EX50 480 120 400 EX51 480 120 400 EX52 480 120 400 EX53 480 120 400 EX54 320 80 600 EX55 768 192 240 EX56 576 144 480 EX57 384 96 720

The samples underwent HCST2 testing, and the results are represented in Table 10. The actual thickness of the samples was measured by ASTM D5736-95 with the fiberglass fabric sheets removed. The plate pressure was calibrated at 0.002 psi (13.790 Pascal).

TABLE 10 Hot-side/Cold-side Temperature Test Results Target Actual Target Basis Actual Basis Thickness Thickness Weight Weight t(150° C.) (mm) (mm) (gsm) (gsm) (seconds) EX41 1.00 0.99 400 387 35 EX42 1.00 0.97 400 337 53 EX43 1.00 1.09 400 324 287 EX44 2.00 1.94 800 547 277 EX45 2.00 1.96 800 697 737 EX46 2.00 2.09 800 657 3600 EX47 3.00 2.92 1000 837 230 EX48 3.00 2.80 1000 743 3600 EX49 2.00 2.02 1000 953 799 EX50 3.00 2.83 1000 930 3600 EX51 4.00 3.56 1000 857 3600 EX52 6.00 5.94 1000 907 3600 EX53 8.00 7.78 1000 933 3600 EX54 3.00 2.80 1000 707 3600 EX55 4.00 3.96 1200 1077 685 EX56 4.00 3.90 1200 1097 3600 EX57 4.00 3.90 1200 873 3600

Densities of 1000 gsm samples containing 40% fumed silica (represented in EX48-EX53) were computed by dividing the actual basis weight (gsm) by the actual thickness (mm). Density and the cold side temperature recorded after 3600 seconds of HCST2 testing for EX48-EX53 is represented in Table 11. The table is organized in descending order by measured cold side temperatures.

TABLE 11 Density vs. Cold Side Temperature Density Cold Side Temperature (gsm/mm) ° C. EX49 472 180.9 EX51 241 141.7 EX53 120 140.2 EX52 153 137.3 EX50 329 134.6 EX48 265 130.8

Thermal conductivity testing was performed, and the results are represented in Table 12.

TABLE 12 Thermal Conductivity Test Results Thermal Conductivity W/m · K EX47 0.0531 EX49 0.0708 EX50 0.0481 EX52 0.0508

Surprisingly, it has been found that fumed silica has a higher thermal conductivity than silica aerogel. It is believed that the thermal conductivity of the nonwoven fibrous thermal insulation without the fumed silica particles (i.e., the fiber matrix) is lower than the same fiber matrix with the fumed silica particles.

Additional Embodiments Battery Cell Thermal Runaway Barrier Embodiments

-   -   1. A thermal runaway barrier operatively adapted (i.e.,         designed, configured, shaped and/or dimensioned) or otherwise         suitable for being disposed between adjacent battery cells         (e.g., prismatic- or pouch-type battery cells) of a battery         module or assembly (i.e., a series of battery cells stacked         together in a row) such as that used to power an electric motor         (e.g., like that used in an electric or hybrid vehicle) and for         preventing, stopping or at least significantly slowing down a         thermal runaway event within the battery module or assembly or         between adjacent battery modules or assemblies, the thermal         runaway barrier comprising:         -   only one or more layers of a dry-laid or wet-laid nonwoven             fibrous thermal insulation (e.g., in the form of a mat,             sheet, strip, or three-dimensional thin-walled structure)             comprising a fiber matrix of ceramic or otherwise             nonmetallic (i.e., not a metal, metal alloy, or metal             composite) inorganic fibers;         -   thermally insulative inorganic particles comprising fumed             silica dispersed evenly, uniformly, generally or otherwise             throughout or to the extent permitted by the manufacturing             process (e.g., there can be a little sedimentation of the             particles on the bottom of the mat in both the dry laid and             wet laid processes) within the fiber matrix, and an organic             or inorganic binder (e.g., organic or inorganic adhesive             binder, organic or inorganic binder fibers that are needle             punched, stitched or otherwise mechanically entangled into             the fiber matrix so as to hold together the fiber matrix,             etc.) dispersed evenly, uniformly, generally or otherwise             throughout or to the extent permitted by the manufacturing             process within the fiber matrix so as to bond together the             inorganic filler particles and inorganic fibers or otherwise             hold together the fiber matrix for as long as needed to at             least survive the degree of handling required (e.g., during             the encapsulation process) before being installed between             battery cells;     -   an optional organic (e.g., polymeric, paper, etc.) encapsulation         layer (e.g., one layer or multiple opposing sandwiching layers,         with each layer being in the form of a film, coating, organic         fibrous nonwoven or woven fabric, etc.) enclosing or otherwise         encapsulating all of, a majority of or a portion of at least one         or both major faces and preferably also all of, a majority of or         a portion of the peripheral edge of the layer of nonwoven         fibrous thermal insulation so as to prevent or significantly         reduce the shedding or loss of inorganic fibers or particles         from the encapsulated layer of nonwoven fibrous thermal         insulation; and     -   an optional inorganic (e.g. glass fiber woven fabric of 25-80         g/m²) encapsulation layer (e.g., one layer or multiple opposing         sandwiching layers, with each layer being in the form of an         inorganic coating or fibrous nonwoven or woven fabric, etc.)         enclosing or otherwise encapsulating all of, a majority of or a         portion of at least one or both major faces and preferably also         all of, a majority of or a portion of the peripheral edge of the         layer of nonwoven fibrous thermal insulation so as to prevent or         significantly reduce the shedding or loss of inorganic fibers or         particles from the encapsulated layer of nonwoven fibrous         thermal insulation.

The reduction of inorganic fiber or particle shedding is significant, when the number of inorganic fibers or particles lost is less than 10%, 5% or 1% by weight percent of the original fiber or particle content of the layer of nonwoven fibrous thermal insulation. The thinner the organic encapsulation layer (i.e., the lower the organic content of the barrier) the better the hot/cold test results.

The present thermal runaway barrier may also be used between battery modules or assemblies.

Inorganic binders, organic binders, or a combination of both can be useful according to the present invention and may include, e.g., those disclosed in U.S. Pat. No. 8,834,759. An example of an inorganic binder useful in both dry-laid or wet-laid fiber processing can include particles of silicone that convert to fusible silica when heated. An organic-inorganic hybrid binder may also be useful such as, e.g., WACKER® MQ 803 TF, which is a co-hydrolysis product of tetra-alkoxy silane (Q unit) and trimethyl-alkoxy silane (M unit). The chemical structure of WACKER® MQ 803 TF can be seen as a three dimensional network of polysilicic acid units which are end-blocked with trimethylsilyl groups. Some residual ethoxy and hydroxy functions are present. The average molecular weight can be exactly controlled by the ratio of M and Q units. This ratio approx. is 0.67 for WACKER® MQ 803 TF.

Exemplary binder fibers include the use of bicomponent core-sheath polymeric fibers in a dry-laid process. In a wet-laid process, ethylene vinyl acetate latex dispersion binder, bicomponent core-sheath polymeric fibers, or a combination of both can be used. When a polymeric binder fiber is used, the binder can be activated by heating and compressing the nonwoven fibrous thermal insulation material. A combination of organic and inorganic binders can also be used.

As used herein, the term “inorganic” refers to ceramic or otherwise nonmetallic (i.e., not a metal, metal alloy, or metal composite) inorganic material.

A “thermal runaway” is when a battery cell experiences an exothermic chain reaction causing the phenomenon of an uncontrollable temperature rise of the battery cell. The exothermic chain reaction may be caused, for example, by over-heating of the battery cell, over-voltage of the battery cell, and mechanical puncture of the battery cell, among other reasons.

A “thermal propagation” is when a battery cell thermal runaway causes the remaining battery cells in a battery pack or system to undergo the thermal runaway phenomenon.

A “thermal runaway event” refers to the overheating of one battery cell, in a container of battery cells, causing a chain reaction of adjacent battery cells overheating, and potentially exploding or catching fire, until the number of overheated battery cells reaches a critical point of propagation resulting in all or more than half of the battery cells in the module or assembly of modules being destroyed. Factors that can cause a battery cell to overheat include: physical damage, applying over voltage, overheating (internal battery cell shorting).

As the energy density of a battery cell increases, the temperature at which the battery cell starts to malfunction (e.g., from at least losing its efficiency or failing to function up to igniting, burning or exploding) decreases. Likewise, as the energy density of the battery cell decreases, the temperature at which the battery cell starts to malfunction increases. For example, with a controlled ramping up of the temperature, NMC811 type battery cells tend to start malfunctioning or even blow up when the temperature reaches around 120° C. to 130° C., while NMC622 type battery cells start to malfunction or even blow up when they reach a temperature of around 180° C. The corresponding temperature is higher for battery cells with lower energy densities (e.g., NMC532 and NMC433 type battery cells). With physically larger battery cells or when the temperature is rapidly increased, thermal diffusion through the battery cell can result in the localized temperature taking longer to get up to the critical point. It is believed that this thermal diffusion effect can cause the actual temperature at which the battery cell starts to malfunction or blow up to be somewhat higher. It can be desirable for the thermal runaway barrier of the present invention to prevent an adjacent battery from reaching a temperature in the range of from about 130° C. up to about 150° C.

As used herein, “preventing” a thermal runaway event refers to preventing the overheating of a single battery cell from causing the overheating of battery cells that are adjacent to the single battery cell. The barrier is considered to prevent a thermal runaway event, when adjacent battery cells do not reach above 130° C., 135° C., 140° C., 145° C. or 150° C.

As used herein, “stopping” a thermal runaway event refers to the overheating of a battery cell only causing adjacent battery cells (i.e., three, two or even only one battery cell away on either side of the overheating battery cell) to overheat and the remaining battery cells in the battery module or assembly do not overheat.

As used herein, “slowing down” a thermal runaway event refers to the thermal runaway event being slowed down at least long enough to allow personnel adjacent to the battery module or assembly (e.g., an occupant inside of an electric vehicle passenger compartment) to escape to a safe distance away from the battery module or assembly, before being injured by the thermal runaway event. Once a battery cell malfunctions (e.g., is on fire or overheats to the point of not functioning) and a thermal barrier is in place between battery cells, the time for any adjacent battery cells to propagate the malfunction (e.g., catching fire or overheating) is at least more than 5 minutes, and preferably more than 10 minutes or even 20 minutes.

-   -   2. The thermal runaway barrier according to embodiment 1,         wherein the particles of fumed silica have a surface area in the         range of from about 100 m²/g up to about 400 m²/g.

The inorganic particles can include, e.g., particles of irreversibly or permanently expanded intumescent material, irreversibly or permanently expanded perlite mineral, etc. Such inorganic particles that contain voids such as, e.g., those found in irreversibly or permanently expanded vermiculite are particularly desirable. Particles of irreversibly or permanently expanded perlite mineral also contain voids, but perlite mineral is harder and less compressible than vermiculite mineral.

As used herein, an irreversibly or permanently expanded expandable particle (e.g., particle of an intumescent material such as vermiculite and perlite mineral) refers to a particle that has been heated to a temperature and for a time that causes the particle to irreversibly or permanently expand to at least 10% and up to 100% of its expandability, either by being pre-expanded before being used to form the thermal runaway barrier, or post-expanded after it is incorporated into the nonwoven fibrous thermal insulation.

Intumescent particles (e.g., vermiculite particles) can be permanently expanded by overheating the particles to beyond the point of reversibility (e.g., in the range of from about 350° C. up to about 1000° C. for vermiculite). Such a permanently expanded intumescent particle (e.g., vermiculite particle) can have an expanded accordion or worm-like structure that is easier to break apart into smaller particles, compared to the same particle in its unexpanded state, because of its elongated geometry, lower density and lower mechanical stability. As the heating temperature increases, the degree of permanent expansion of the particle increases (i.e., the particles can get larger and/or longer). It may also be desirable to use vermiculite that has been permanently expanded by a chemical treatment method (see, e.g., “Chemical Exfoliation of Vermiculite and the Production of Colloidal Dispersions”, G. F. Walker, W. G. Garrett, Science 21 Apr. 1967: Vol. 156, Issue 3773, pp. 385-387, DOI: 10.1126/science. 156.3773.385; and https://science.sciencemag.org/content/156/3773/385.abstract).

Because they are easier to break apart in their expanded state, it can be desirable to post-expand the intumescent particles, after the unexpanded intumescent particles have been incorporated into the nonwoven fibrous thermal insulation. Even if gentle processing is employed so as not to substantially break them apart, it is believed that incorporating pre-expanded intumescent particles into the nonwoven fibrous thermal insulation can still result in the expanded particles becoming oriented into the plane (i.e., x-axis, y-axis, and/or therebetween) of the insulation. For example, with pre-expanded vermiculite particles, the elongated particles can become generally aligned with the fibers in the longitudinal or downstream direction (i.e., y-axis), rather than in the thickness direction (i.e., z-axis), of the nonwoven fibrous thermal insulation.

In contrast, when they are post-expanded (i.e., after the nonwoven fibrous thermal insulation is made with unexpanded intumescent particles), the expanded intumescent particles are not oriented primarily in the plane of the insulation. Unexpanded intumescent particles typically have a more uniform structural geometry (i.e., have an aspect ratio closer to 1) compared to the same particles in its expanded state. It is believed that this more uniform structural geometry is less likely to be influenced by the alignment of the fibers during the formation of the nonwoven fibrous thermal insulation. As a result, the post-expanded intumescent particles are more likely to be oriented isotropically within the nonwoven fibrous thermal insulation. For example, with post-expanded vermiculite particles, the elongated particles can become aligned in the thickness direction (i.e., z-axis), in plane (i.e., x-axis, y-axis, and/or therebetween), or off-axis thereof. It is believed this difference between the orientation of pre-expanded particles versus post-expanded particles is caused by the unexpanded particles having a more uniform structural geometry than that exhibited while in their expanded state.

-   -   3. The thermal runaway barrier according to embodiment 1 or 2,         wherein the layer of nonwoven fibrous thermal insulation         contains an amount of inorganic fibers in the range of from as         low as about 15 to 19% up to as high as about 70, 75, 80, 85 or         90%, by weight of the layer of nonwoven fibrous thermal         insulation.     -   4. The thermal runaway barrier according to any one of         embodiments 1 to 3, wherein the layer of nonwoven fibrous         thermal insulation contains an amount of fiber shot in the range         of from about 3% up to about 60% by weight of the amount of         inorganic fibers in the layer of nonwoven fibrous thermal         insulation.

In one embodiment, if no insulative particles are added, then inorganic fiber content is 95.2% by weight in dry-laid and 95.5% by weight in wet-laid. At the lowest level of insulative particle (e.g., aerogel particle) loading, the inorganic fiber content is 72% by weight for dry-laid and wet-laid. For dry laid nonwoven fibrous thermal insulation, the fibers are opened (i.e., the bulk fibers are separated, made less dense), which may remove some shot. For wet laid nonwoven fibrous thermal insulation, the fibers are wet cleaned, which removes more shot than is removed by the dry laid opening process. There is about 40% shot in uncleaned SuperWool Plus from Morgan, actual fibrous material content is 19-43% in the nonwoven fibrous thermal insulation. It can be desirable for the nonwoven fibrous thermal insulation to have a fiber content in the range of from about 10% up to about 80%. The lower amount of fiber would require a higher amount of organic binder. Other additives (e.g., flame retardant materials, endothermic materials, infra-red reflective materials, etc.) may be included.

-   -   5. The thermal runaway barrier according to any one of         embodiments 1 to 4, wherein the layer of nonwoven fibrous         thermal insulation contains an amount of the thermally         insulative inorganic particles in the range of from as low as         about 10%, 15%, 20%, 25%, 30% or 35% up to as high as about 40%,         45%, 50%, 55% or 60%, by weight of the layer of nonwoven fibrous         thermal insulation. For example, a particle content as high as         60% can be achieved using a dry-laid process, and as high as 50%         using a wet laid process.     -   6. The thermal runaway barrier according to any one of         embodiments 1 to 5, wherein the layer of nonwoven fibrous         thermal insulation contains an amount of organic binder in the         range of from as low as about 2.5%, 3.0%, 3.5%, 4.0%, 4.5%,         5.0%, 5.5%, 6.0% or 6.5% up to as high as about 7.0%, 7.5%,         8.0%, 8.5%, 9.0%, 9.5%, or 10.0%, by weight of the layer of         nonwoven fibrous thermal insulation.     -   7. The thermal runaway barrier according to any one of         embodiments 1 to 6, wherein the layer of nonwoven fibrous         thermal insulation has an installed (i.e., compressed) thickness         in the range of from about 0.5 mm up to less than 5.0 mm. In         particular, the installed (i.e., compressed) thickness in the         range of from about 0.5 mm up to about 2.5 mm, where the lower         limit can be about 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0         mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, and the upper limit         can be about 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2         mm, 2.3 mm, 2.4 mm or 2.5 mm. In some applications, the         installed thickness may even be as high as about 2.6 mm, 2.7 mm,         2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm,         3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm,         4.4 mm, 4.5 mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm or less than         5.0 mm. The installed thickness of the layer of nonwoven fibrous         thermal insulation is almost always less than its uninstalled         (i.e., uncompressed) thickness. The performance of the thermal         runaway barrier is measured when it is in its installed (i.e.,         compressed) condition.     -   8. The thermal runaway barrier according to any one of         embodiments 1 to 7, wherein the layer of nonwoven fibrous         thermal insulation has an uninstalled (i.e., uncompressed)         thickness in the range of from about 1.0 mm up to less than 8.0         mm, where the lower limit can be about 1.0 mm, 1.1 mm, 1.2 mm,         1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm,         2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm,         2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, or 3.5 mm, and         the upper limit can be about 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4         mm, 4.5 mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm, 5.0 mm, 5.5 mm, 6.0         mm, 6.5 mm, 7.0 mm, 7.5 mm, or 8.0 mm. The uncompressed         thickness of the layer of nonwoven fibrous thermal insulation is         always greater than its installed thickness.     -   9. The thermal runaway barrier according to any one of         embodiments 1 to 8, wherein the layer of nonwoven fibrous         thermal insulation has a basis weight in the range of from as         low as about 250 g/m² up to as high as about 1000 g/m².         Depending on the composition of the thermal runaway barrier, it         can be desirable for the basis weight to be in the range of from         about 250 g/m² to about 400 g/m² (e.g., 300 g/m², 350 g/m²) for         a gap between adjacent battery cells in the range of from about         0.75 mm up to about 1.25 mm. Depending on the composition of the         thermal runaway barrier, it can also be desirable for the basis         weight to be in the range of from about 300 g/m² up to about 550         g/m² for a gap between adjacent battery cells in the range of         from about 0.75 mm to about 2.5 mm, and up to as high as about,         For gaps between adjacent battery cells in the range of from         about 2.5 mm up to less than 5.0 mm, it can be desirable for the         basis weight to be in the range of from about 600 g/m² up to         about 1000 g/m² (e.g., about 650 g/m², 700 g/m², 750 g/m², 800         g/m², 850 g/m², 900 g/m², 950 g/m² or 1000 g/m²). Desirable         results have been achieved with thermal runaway barriers using         thermally insulative inorganic particles of irreversibly or         permanently expanded vermiculite, where the nonwoven fibrous         thermal insulation has a basis weight of about 450 g/m² or 550         g/m² for a gap in the range of from about a 1.50 mm up to about         2.5 mm.

In one embodiment, the thermally insulative inorganic particles are particles of irreversibly or permanently expanded vermiculite, and the layer of nonwoven fibrous thermal insulation has a basis weight of 450 g/m² for an installed gap between adjacent battery cells in the range of from about a 1.50 mm up to about 2.5 mm. In another embodiment, the thermally insulative inorganic particles are particles of irreversibly or permanently expanded vermiculite, and the layer of nonwoven fibrous thermal insulation has a basis weight of 550 g/m² for an installed gap between adjacent battery cells in the range of from about a 1.50 mm up to about 2.5 mm.

-   -   10. The thermal runaway barrier according to any one of         embodiments 1 to 9, wherein the layer of nonwoven fibrous         thermal insulation has a basis weight in the range of from about         250 g/m² up to about 400 g/m².

In a particular embodiment, for example, a basis weight in the range of from about 300 g/m² up to 400 g/m² can be desirable, when the thermally insulative inorganic particles are particles of irreversibly or permanently expanded vermiculite and the gap is about 1 mm. When the gap is about 2.0 mm, a basis weight in the range of from about 800 g/m² up to about 1000 g/m² may be desirable.

-   -   11. The thermal runaway barrier according to any one of         embodiments 1 to 10, wherein the thermally insulative inorganic         particles are made from or at least comprise particles of one or         any combination of the materials selected from the group         consisting of irreversibly or permanently expanded vermiculite         (i.e., vermiculite that has been heated to a temperature and for         a time that causes the vermiculite particles to irreversibly or         permanently expand to at least 10% and up to 100% of its         expandability, either by being pre-expanded before being used to         form the barrier, or post-expanded after it is in the nonwoven         fibrous thermal insulation), irreversibly or permanently         expanded perlite (i.e., perlite that has been heated to a         temperature and for a time that causes the perlite particles to         irreversibly or permanently expand to at least 10% and up to         100% of its expandability, either by being pre-expanded before         being used to form the barrier, or post-expanded after it is in         the nonwoven fibrous thermal insulation), and irreversibly or         permanently expanded clay.

Expanded clay is a lightweight particle or aggregate, which can be made by heating clay to around 1,200° C. (2,190° F.) in a rotary kiln. The yielding gases expand the clay by thousands of small bubbles forming during heating producing a honeycomb structure. Expanded clay can have an approximately round or potato shape due to circular movement in the kiln and is available in different sizes and densities. Expanded clays have been used to make lightweight concrete products (see, e.g., the website: https://www.archiexpo.com/architecture-design-manufacturer/expanded-clay-aggregate-concrete-23000.html) and other uses. Expanded clay is most commonly known under the brand names LECA (acronym of light expanded clay aggregate) or LIAPOR (porous has clay), also known as Hydroton and under the non-proprietary terms fired clay pebble, grow rocks, expanded clay or hydrocorns, are small globes of burnt and expanded clay (see, e.g., the website: https://www.sciencedirect.com/topics/engineering/expanded-clay-aggregate).

It can be desirable for the thermal runaway barrier to further include other thermally insulative inorganic particles such as, e.g., particles of one or any combination of the materials selected from the group consisting of inorganic aerogel, xerogel, hollow or porous ceramic microspheres, unexpanded vermiculite, otherwise porous silica, unexpanded perlite, pumicite, diatomaceous earth, titania and zirconia.

-   -   12. The thermal runaway barrier according to any one of         embodiments 1 to 11, wherein the inorganic fibers of the fiber         matrix are selected from the group of fibers consisting of         alkaline earth silicate fibers, refractory ceramic fibers (RCF),         polycrystalline wool (PCW) fibers, basalt fibers, glass fibers         and silicate fiber. Glass fibers and silica fibers typically do         not contain any or only nominal shot particles. PCW typically         contains a max of 5% shot particles, while alkaline earth         silicate (AES) fibers contain up to 60% shot particles when         uncleaned and as low as about 10-30% minimum shot particles when         cleaned).     -   13. The thermal runaway barrier according to any one of         embodiments 1 to 12, wherein the organic binders are in the form         of polymer fibers (e.g., PE/PET, PET, FRPET), dry polymer powder         (e.g., LDPE, polyamide, epoxy resin powder (3M SCOTCHCAST 265,         3M SCOTCHKOTE 6258)) or a liquid binder (e.g., acylic latex,         ethylene vinyl acetate (EAF68) latex, silicone, polyurethane         etc.).     -   14. The thermal runaway barrier according to any one of         embodiments 1 to 13, wherein the layer of nonwoven fibrous         thermal insulation is encapsulated by the organic encapsulation         layer.     -   15. The thermal runaway barrier according to embodiment 14,         wherein the organic encapsulation layer has at least one vent         hole formed therethrough that is located and sized to allow         expanding gas (e.g., air) contained within the thermal runaway         barrier to escape from the organic encapsulation, such that the         structural integrity of the organic encapsulation layer is kept         intact (i.e., the layer of nonwoven fibrous thermal insulation         remains completely, mostly or at least significantly         encapsulated by the organic encapsulation layer), when the         thermal runaway barrier is compressed during the assembly of the         battery cell module (e.g., a stack of battery cells) or when the         thermal runaway barrier heats up (e.g., during the normal         operation or overheating of the adjacent battery cells). Each         vent hole can be in the shape of a rectangle (e.g., see FIG. 8         ), circle, oval or any other shape desired or combination         thereof. One or more or each vent hole can be in the form of a         notch that projects from a side edge of the encapsulation         towards the center of the thermal runaway barrier (e.g., see the         left side vent hole 54 in FIG. 8 and the vent holes 54 in FIG. 7         ). Alternatively, one or more or each vent hole can be formed         interior of the side edge of the encapsulation and adjacent to         the nonwoven thermal insulation (see the right side vent hole 52         in FIG. 8 and the vent holes 52 in FIG. 6 ). In addition, one or         more or each vent hole can be formed through the encapsulation         layer on only one side (see vent hole 52 on the right side of         FIG. 6 ) or both sides (see vent hole 52 on the left side of         FIG. 6 ) of the nonwoven fibrous thermal insulation. It can also         be desirable for each vent hole to be in the form of a plurality         of small perforation, that are clustered together (e.g., like a         screen, sieve or colander) to provide the desired exit opening         area.     -   16. The thermal runaway barrier according to embodiment 14 or         15, wherein the thermal runaway barrier has a top edge, a bottom         edge and opposite side edges, and the at least one vent hole is         located along the periphery of one or both opposite side edges.     -   17. The thermal runaway barrier according to any one of         embodiments 14 to 16, wherein the at least one vent hole         provides an exit opening through the organic encapsulation layer         having an opening area in the range of from about 2 mm² up to         about 15 mm². It is contemplated that any particular area within         this range, or any narrower range within this range, could be         desirable.     -   18. The thermal runaway barrier according to any one of         embodiments 14 to 17, wherein the organic encapsulation layer is         in the form of a continuous layer, a discontinuous layer (e.g.,         having perforations, through-holes, or porosity that would allow         a gas to penetrate through the organic layer), or a combination         of both. In addition, the organic layer can be in the form of an         organic (e.g., polymeric) film, scrim, woven or nonwoven fabric,         adhesive (e.g., a thermoplastic or hot-melt adhesive) layer or a         combination thereof. One example of the organic layer is a         polymeric film (e.g., a co-polyester polymeric film).     -   19. The thermal runaway barrier according to any one of         embodiments 14 to 18, wherein the organic encapsulation layer is         a calendared layer, hot-melt coated layer, spray coated layer,         dip coated layer, or laminated layer (e.g., with by use of a         pressure sensitive adhesive or other adhesive).     -   20. The thermal runaway barrier according to any one of         embodiments 14 to 19, wherein the layer of nonwoven fibrous         thermal insulation has a peripheral edge, and the organic         encapsulation layer is sealed around the peripheral edge.     -   21. The thermal runaway barrier according to any one of         embodiments 1 to 20, wherein the layer of nonwoven fibrous         thermal insulation passes at least the V-2 or V-1 level, and         preferably the V-0 level, of the below UL94 V0 Flammability         Test.

Flammability Test

The test was performed using the UL-94 standard, the Standard for safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing. The UL-94 standard is a plastics flammability standard released by Underwriters Laboratories of the United States. The standard determines the material's tendency to either extinguish or spread the flame once the specimen has been ignited. The UL-94 standard is harmonized with IEC 60707, 60695-11-10 and 60695-11-20 and ISO 9772 and 9773. A 75 mm×150 mm sample was exposed to a 2 cm, 50 W tirrel burner flame ignition source. The test samples were placed vertically above the flame with the test flame impinging on the bottom of the sample. For each sample, the time to extinguish was measured and V ratings are assigned. V ratings are a measure to extinguish along with the sample not burning to the top clamp or dripping molten material which would ignite a cotton indicator, as shown in Table 1 below.

TABLE 1 UL94 classification (V rating). UL 94 classification V-0 V-1 V-2 Burning stops within 10 s 30 s 30 s Drips of burning material allowed No No Yes (ignites cotton ball) Total burn of sample No No No

-   -   22. The thermal runaway barrier according to any one of         embodiments 1 to 21, wherein the thermally insulative inorganic         particles at least comprise particles of irreversibly or         permanently expanded intumescent material.     -   23. The thermal runaway barrier according to embodiment 22,         wherein the expanded intumescent material has been irreversibly         or permanently expanded in the range of from at least about 10%,         20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% up to 100% of its         expandability.     -   24. The thermal runaway barrier according to any one of         embodiments 1 to 23, wherein the thermally insulative inorganic         particles at least comprise particles that are irreversibly or         permanently expanded vermiculite particles.     -   25. The thermal runaway barrier according to embodiment 24,         wherein the expanded vermiculite particles have been         irreversibly or permanently expanded in the range of from at         least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% up to         100% of its expandability.     -   26. A thermal runaway barrier assembly comprising a plurality of         the thermal runaway barriers according to any one of embodiments         1 to 25, wherein the plurality of thermal runaway barriers are         provided (a) in a container (e.g., a cardboard or other box) in         the form of a stack, (b) disposed end-to-end in series, with one         major face of each thermal runaway barrier being adhered onto a         major adhesive surface of a length of single-sided or         double-sided adhesive tape (When a double-sided adhesive tape is         used, the opposite major adhesive surface of the tape can be         protected by a release liner), or (c) disposed end-to-end in         series in the form of a tape, with the one or more layers of         nonwoven fibrous thermal insulation of each thermal runaway         barrier being disposed end-to-end and sandwiched or otherwise         encapsulated between two opposing lengths of organic (e.g.,         polymeric) encapsulation layers (e.g., in the form of two         opposing films, coatings, fibrous fabrics, etc.).

Battery Cell Module Embodiments

-   -   27. A battery cell module or assembly for an electric vehicle,         the battery cell module or assembly comprising:         -   a plurality of battery cells disposed in a housing; and         -   a plurality of thermal runaway barriers according to any one             of embodiments 1 to 26,         -   wherein the battery cells are lined up in a row or stack,             with one thermal runaway barrier being disposed between each             pair of adjacent battery cells or between a predetermined             number of battery cells.

Method of Making Battery Cell Thermal Runaway Barrier Embodiments

-   -   28. A method of making the thermal runaway barrier according to         any one of embodiments 1 to 27, wherein the method comprises         forming the layer of nonwoven fibrous thermal insulation using a         wet-laid process or dry-laid process.     -   29. The method according to embodiment 28, further comprising:         -   providing thermally insulative inorganic particles that are             made completely of, mostly of or at least comprise fumed             silica;         -   disposing the thermally insulative inorganic particles so as             to be evenly or uniformly distributed throughout or within             the layer of nonwoven fibrous thermal insulation.     -   30. The method according to embodiment 29, further comprising:         -   providing additional thermally insulative inorganic             particles that are made completely of, mostly of or at least             comprise unexpanded expandable particles (e.g., unexpanded             intumescent particles such as unexpanded vermiculite             particles or unexpanded perlite particles);         -   disposing the unexpanded expandable particles so as to be             evenly or uniformly distributed throughout or within the             layer of nonwoven fibrous thermal insulation; and         -   heating the unexpanded expandable particles (e.g.,             intumescent particles) to a temperature and for a time that             causes the unexpanded expandable particles to irreversibly             or permanently expand, wherein the heating occurs before or             after the unexpanded expandable particles are disposed             within the layer of nonwoven fibrous thermal insulation.     -   31. The method according to embodiment 30, wherein the heating         occurs after the unexpanded expandable particles are disposed         within the layer of nonwoven fibrous thermal insulation.     -   32. The method according to embodiment 30 or 31, wherein the         heating causes the unexpanded intumescent particles to         irreversibly or permanently expand in the range of from at least         about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% up to 100%         of their expandability.     -   33. The method according to any one of embodiments 30 to 32,         wherein the unexpanded expandable particles include unexpanded         intumescent particles (e.g., vermiculite particles, unexpanded         perlite particles, or a combination of both).     -   34. The method according to embodiment 29, further comprising:         -   providing thermally insulative inorganic particles that are             made completely of, mostly of, or at least comprise             irreversibly or permanently pre-expanded expandable             particles (e.g., irreversibly or permanently pre-expanded             intumescent particles of vermiculite or perlite); and         -   disposing the thermally insulative inorganic particles so as             to be evenly or uniformly distributed throughout or within             the layer of nonwoven fibrous thermal insulation,         -   wherein the pre-expanded particles where formed by heating             unexpanded expandable particles to a temperature and for a             time that causes the unexpanded expandable particles to             irreversibly or permanently expand, before the thermally             insulative inorganic particles are disposed within the layer             of nonwoven fibrous thermal insulation.     -   35. The method according to embodiment 34, wherein the         pre-expanded expandable particles are intumescent particles that         are irreversibly or permanently expanded in the range of from at         least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% up to         100% of their expandability.     -   36. The method according to embodiment 34 or 35, wherein the         pre-expanded expandable particles include pre-expanded         vermiculite particles, pre-expanded perlite particles, or both.

This invention may take on various modifications and alterations without departing from its spirit and scope. For example, it is believed that microwave heating can be used to irreversibly or permanently expand the particles made from intumescent materials. It is also believed that using microwave energy, rather than baking in an oven, can result in a more uniform expansion of the intumescent particles within the fiber matrix. Accordingly, this invention is not limited to the above-described but is to be controlled by the limitations set forth in the following embodiments and any equivalents thereof. This invention may be suitably practiced in the absence of any element not specifically disclosed herein. All patents and patent applications cited above, including those in the Background section, are incorporated by reference into this document in total. 

1. A thermal runaway barrier operatively adapted for being disposed between battery cells of a battery assembly and for at least significantly slowing down a thermal runaway event within the battery assembly, said thermal runaway barrier comprising: a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers; thermally insulative inorganic particles of fumed silica material dispersed within the fiber matrix, and a binder dispersed within the fiber matrix so as to hold together the fiber matrix; an optional organic encapsulation layer enclosing the layer of nonwoven fibrous thermal insulation; and an optional inorganic encapsulation layer enclosing the layer of nonwoven fibrous thermal insulation.
 2. The thermal runaway barrier according to claim 1, wherein the particles of fumed silica have a surface area in the range of from about 100 m²/g up to about 400 m²/g.
 3. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation contains an amount of fiber shot in the range of from about 3% up to about 60% by weight of the amount of inorganic fibers in the layer of nonwoven fibrous thermal insulation.
 4. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation contains an amount of thermally insulative inorganic particles in the range of from as low as about 10% up to as high as about 60%, by weight of the layer of nonwoven fibrous thermal insulation.
 5. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation contains an amount of organic binder in the range of from as low as about 2.5% up to as high as about 10.0%, by weight of the layer of nonwoven fibrous thermal insulation.
 6. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation has an installed thickness in the range of from about 0.5 mm up to less than 5.0 mm.
 7. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation has a basis weight in the range of from as low as about 250 g/m² and up to as high as about 1000 g/m².
 8. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation has an uncompressed basis weight in the range of from about 250 g/m² up to about 400 g/m².
 9. The thermal runaway barrier according to claim 1, wherein the thermally insulative inorganic particles further comprise particles of one or any combination of the materials selected from the group consisting of inorganic aerogel, xerogel, hollow or porous ceramic microspheres, unexpanded vermiculite, irreversibly or permanently expanded vermiculite, otherwise porous silica, irreversibly or permanently expanded perlite, unexpanded perlite, pumicite, expanded clay, diatomaceous earth, titania and zirconia.
 10. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation is encapsulated by the organic encapsulation layer.
 11. The thermal runaway barrier according to claim 10, wherein the organic encapsulation layer has at least one vent hole formed therethrough that is located and sized to allow gas contained within the thermal runaway barrier to escape from the organic encapsulation, such that the structural integrity of the organic encapsulation layer is kept intact, during a thermal runaway event.
 12. The thermal runaway barrier according to claim 10, wherein the thermal runaway barrier has a top edge, a bottom edge and opposite side edges, and the at least one vent hole is located along the periphery of one or both opposite side edges.
 13. The thermal runaway barrier according to claim 10, wherein the at least one vent hole provides an exit opening through the organic encapsulation layer having an opening area in the range of from about 2 mm² up to about 15 mm².
 14. The thermal runaway barrier according to claim 10, wherein the layer of nonwoven fibrous thermal insulation has a peripheral edge, and the organic encapsulation layer is sealed around the peripheral edge.
 15. The thermal runaway barrier according to claim 1, wherein the layer of nonwoven fibrous thermal insulation passes at least the V-2 level of the UL94 Flammability Test.
 16. The thermal runaway barrier according to claim 1, wherein the thermally insulative inorganic particles comprise particles of irreversibly or permanently expanded intumescent material.
 17. The thermal runaway barrier according to claim 1, wherein the thermally insulative inorganic particles comprise particles of irreversibly or permanently expanded vermiculite.
 18. The thermal runaway barrier according to claim 17, wherein the expanded vermiculite has been irreversibly or permanently expanded in the range of from at least about 10% up to 100% of its expandability.
 19. A battery cell module for an electric vehicle, said battery cell module comprising: a plurality of battery cells disposed in a housing; and a plurality of thermal runaway barriers according to claim 1, wherein the battery cells are lined up in a row, with one thermal runaway barrier being disposed between each pair of adjacent battery cells.
 20. A method of making the thermal runaway barrier according to claim 1, wherein said method comprises: forming the layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process. 